The invention relates to a method of regenerating start-stop signals of a type having a stop polarity which is maintained for a certain period of time T after a start-stop transition, T being either greater than or equal to a minimum value, or greater than or equal to a minimum value and smaller than or equal to a maximum value, and of converting the regenerated signals into isochronous output signals, signal samples of the start-stop signals being taken at consecutive sampling instants by means of a regeneration process initiated by the start-stop transition, said signal samples being consecutively stored in a storage device which is read at isochronous instants for forming the isochronous output signals.
The invention also relates to an arrangement for performing a method of the above type.
The invention has application in the field of multiplexing telex signals in accordance with CCITT recommendation R101, wherein one element of a telex signal is represented by one bit in the isochronous signal. The regeneration process used in the multiplexer and based on sampling the consecutive elements is synchronized by the occurrence of each stop-start transition.
The telex signals used for signalling, more particularly those signals which consist of a stop polarity which is maintained for a certain period of time after a start-stop transition, do not have the form of characters and therefore render special measures necessary for their regeneration. It is common practice to start, initiated by the start-stop transition, a regeneration process having consecutive sampling instants which occur at equal time intervals. When this regeneration process is used in tandem arrangements of a plurality of transmission systems wherein alternately the telex signals are converted into isochronous signals and the isochronous signals, by means of direct restitution into telex signals the problem is encountered that the transmission of a signalling pulse of a minimum duration can result in the production at the output of the demultiplexer, after the first repetition of the regeneration process, of a signalling pulse which has a duration which is less than the minimum duration recommended by the CCITT for signalling pulses to be received.
Such signalling pulses are not suitable for further transmission. The realisation of tandem arrangements then require additional measures to increase the pulse duration, or a direct restitution of the telex signals from the isochronous signal is no longer sufficient.